This application claims the priority of German Patent Application Serial No. 101 32 970.9, filed Jul. 6, 2001, pursuant to 35 U.S.C. 119(a)-(d), the subject matter of which is incorporated herein by reference.
The present invention relates, in general, to a mold mounting plate for an injection molding machine.
U.S. Pat. No. 5,593,711 describes a mold mounting plate for support of a mold of a plastics injection molding machine. The mold mounting plate includes a base plate, a frustoconical center portion, and a front plate in parallel relationship to the base plate. The base plate has corner regions provided with bores for receiving four tie bars of the injection molding machine. The center portion is configured as hollow body and has a base for attachment to a central location of the base plate. The blunted tip of the central portion is attached to the front plate for the mold. Thus, the front plate is supported solely in its central area by the center portion. In this way, the front plate of the mold mounting plate is intended to remain flat, even when subjected to the clamping force of the injection molding machine, to thereby prevent a deflection and resultant opening of the mold halves.
European Pat. No. EP 0 789 648 B1 discloses an injection molding machine having a substantially C-shaped machine frame having two limbs, which are not connected by tie bars. Mounted to one of the limbs is a fixed mold mounting plate, whereas a flange of a closing unit is secured to the other limb. The closing unit essentially includes a hydraulic piston and cylinder unit to shift the moveable mold mounting plate, which is displaceably supported on the machine frame. The flange and the fixed mold mounting plate are each secured by holding members to the limbs of the machine frame. During closing operation, the holding members of the flange are subject to tensile stress and the fixed mold mounting plate is subject to pressure. The holding members are functionally equivalents to springs and have an elasticity, which is smaller than the elasticity of the machine frame. Several holding members may be provided in spaced-apart disposition over the height of the fixed mold mounting plate and the flange and exhibit different elasticity, whereby the lower holding members have a greater elasticity than the upper holding members. The holding members are made of spring steel and weakened through provision of slots. Their lower portion has slots of different depth to enhance the elasticity. When the limbs of the machine frame are pushed apart in the upper zone during injection operation, the fixed mold mounting plate and the flange can tilt relative to the machine frame to maintain the mold mounting plates in parallel relationship. The holding members thus form an axleless joint to allow rotational motions as well as translational motions.
European Pat. No. EP 0 381 107 B1 discloses a closing unit for a horizontal two-platen injection molding machine for processing plastic material. The injection molding machine includes a fixed mold mounting plate and a moveable mold mounting plate in confronting disposition to support respective mold halves of the mold. The fixed mold mounting plate has a substantially rectangular configuration and is connected with the moveable mold mounting plate by four spindles positioned in the corners of an imaginary tetragon. The spindles are non-rotatably arranged and cantilevered on the fixed mold mounting plate. In order to close and open the mold, the moveable mold mounting plate can be moved in a direction to and away from the fixed mold mounting plate by the spindles, as it travels along the spindles. The drive for the moveable mold mounting plate is implemented by mounting on the side, facing away from the clamping surface for the mold, a spindle nut for each of the spindles, whereby all the spindle nuts rotate together in synchronism by a drive, e.g., electric motor. The spindle nuts are each constructed as ball nut. After closing the mold, the clamping force is applied on the mold halves by an additional hydraulic piston and cylinder unit, which acts on the spindle nuts. The piston and cylinder unit has an annular piston through which the respective spindle is guided. In order to allow opening of the mold halves after the injection molding process, the piston and cylinder unit is constructed as a double-action piston and cylinder unit.
When the mold mounting plates distorts or deforms, these deformations are transmitted to the spindles guided in the openings of the mold mounting plate, resulting in undesired bending stress of the spindles so that the parallelism between the spindles and between the spindles and the axis of the injection molding machine is no longer maintained. As a consequence, the spindles and/or the spindle drives are exposed to increased wear, reducing service life and leading ultimately to their destruction.
It would therefore be desirable and advantageous to provide an improved mold mounting plate of an injection molding machine to obviate prior art shortcomings and to minimize in a simple manner a transmission of moments onto column-like holding and/or guiding elements of the injection molding machine as a result of a deformation of the mold mounting plate.
According to one aspect of the present invention, a mold mounting plate for an injection molding machine for processing material, in particular plastic material, includes a main body having a plate-shaped central portion, plural sleeves received in the main body and defining openings for support of column-like holding and/or guiding elements of the injection molding machine, and a connection assembly for securing the sleeves to the central portion such as to establish a flexible bending/torsion joint.
The present invention resolves prior art problems by providing an elastic securement for a connection of the mold mounting plate to the holding and/or guiding elements through dividing the mold mounting plate into a rigid central portion and sleeves, which are supported elastically in the central portion. Suitably, the central portion and the sleeves are made of single-piece configuration, preferably a single-piece structure of cast steel.
According to another feature of the present invention, the central portion of the main body may have a substantially rectangular configuration and defines corner regions for arrangement of the sleeves in one-to-one correspondence, wherein the connection assembly may include in each of the corner regions a pair of legs, arranged in spaced apart relationship to define a U-shaped area and extending outwards, and a bolt arranged between the legs and provided for attachment of the sleeve. Upon application of a clamping force, the legs and the bolts are subjected to torsion and bending. Suitably, the sleeve is secured in midsection of the bolt at its side confronting the center portion. In order to enlarge the contact area between the sleeve and the bolt, the sleeve dips into the bolt, i.e. the sleeve is partly received in the bolt.
According to another feature of the present invention, the central portion may include an inner rib structure having opposite sides, and cover plates, one cover plate covering one side of the rib structure, and the other cover plate covering the other side of the rib structure, wherein the rib structure includes a central annulus, Y-shaped connecting ribs having one end secured to the annulus and being spaced from one another in a star-shaped manner, and peripheral ribs connected to another end of the Y-shaped connecting ribs. Thus, as the mold mounting plate is subjected to the clamping force, the cover plates are no longer required to absorb loads in the area of the flexible joint and thus, there is no need to extend the cover plates beyond the central portion, so that the weight of the mold mounting plate can be reduced.
Through configuration of the mold mounting plate with the rib structure, the stiffness of the mold mounting plate can be suited to the situation at hand by changing the vertical extension and position of the rib structure, so that a self-flexure of the mold mounting plate is minimized during the injection molding process.
A mold mounting plate according to the present invention is suitable for use in plastics injection molding machine without tie bars, whereby the mold mounting plates are connected hereby to the, normally U-shaped, machine frame by holding and/or guiding elements received in the openings of the sleeves. This support of the mold mounting plates without axle joint maintains the parallelism of the mold mounting plates, when the legs of the U-shaped machine frame yield as a result of the clamping force. Of course, a mold mounting plate according to the present invention is also suitable for use in so-called three-platen injection molding machines.
According to another feature of the present invention, the bolt may be arranged in eccentric relationship to the sleeve. Suitably, the sleeve defines a longitudinal axis, which is oriented at a right angle to the surface of the central portion, and the bolt defines a longitudinal axis, which is oriented at a right angle to the surface of the central portion and extends at a right angle to the longitudinal axis of the sleeve.
According to another feature of the present invention, the sleeve may be separated from the central portion by a gap on its outer surface facing the central portion. Suitably, the gap has a sickle-shaped configuration.
According to another feature of the present invention, the legs may be respectively connected to the bolt via rounded transitions, and the bolt is connected to the sleeve via a rounded transition. In this way, the sleeve, the bolt and the legs can be connected together in a notch-friendly manner.